单项选择题
A.load B.substitute C.conservation D.reserve
The ratio of the work done by the machine（）the work don...
单项选择题The ratio of the work done by the machine（）the work done on it is called the efficiency of the machine.
A.against B.with C.to D.for
His inability to learn foreign languages was a(n（）to hi...
单项选择题His inability to learn foreign languages was a(n（）to his career.
A.objection B.defect C.obstacle D.depression
In general , the amount that a student spends for housi...
单项选择题In general , the amount that a student spends for housing should be held to one-fifth the total（）for living expenses.
A.acceptable B.available C.advisable D.applicable
